The present invention generally relates to aircraft communication systems, and more particularly is concerned with extremely high integrity data communication systems for critical aviation information transmitted on a single transmission line.
In recent years, the aviation industry has been involved in a seemingly never ending quest to enhance the safety and performance of modern aircraft. One particular area in which avionics engineers have expended much effort and achieved many successes, is in the substitution of completely electronic systems for the conventional mechanical systems of the past. A prime example of these efforts is in the area of "fly by wire" aircraft. This "fly by wire" concept involves the substitution of electrical and optical systems for the conventional mechanical systems which actuate the most basic flight control such as engine throttle, wing flaps, ailerons, horizontal stabilizer, and rudder functions. In the past, these functions have been typically achieved by connecting cables, gears or levers from the cockpit back through the aircraft fuselage to the actuators. The replacement of these often quite heavy and bulky mechanical systems with smaller and lighter electrical and optical systems has obvious advantages, another not so obvious advantage is that it allows for integration of additional functions i.e. flight envelope protection. These advantages are especially desirable with the current aspirations by airframe manufacturers to produce highly fuel efficient aircraft with enhanced safety characteristics.
Numerous methods for replacing the cables and levers have been proposed, with the most generally accepted idea being to generate redundant electronic signals at the cockpit controls and other sensors which are then processed by multiple independent computational elements. Each computational element or channel produces an output instance. These independent instances make it possible to detect faults such that an output can be judged good or bad with an extremely high level of integrity. Outputs are then transmitted through multiple electrical transmission lines or fiber optics to the actuators. A data transmission system such as this must be of extremely high integrity. Data corruption can occur during the transmission of the signal along the electrical transmission line due to electromagnetic interference from other sources within the aircraft and by, among other things, faults within the transmit or receive devices. Exposure to undetected or latent faults including generic design and manufacturing faults must be eliminated in order to produce an extremely high integrity system.
In the past, in order to ensure that the critical flight control data was unaltered during transmission it would be sent along two or more separate and independent transmission lines. This allowed for a comparison at the receiving end of the data coming down the separate lines.
While this method of dual independent transmission lines has been widely used in the past, it does have several disadvantages. The paramount problem with this conventional approach is in the added weight and installation cost of the dual lines. Also the cost and power requirements of a parallel and separate system is unattractive.
Consequently, a need exists for the improvement in high integrity data communication systems for critical aviation information which does not require the use of separate and independent transmission lines but at the same time retains the integrity of that critical information.